fix(pyplot): robot.plot(..., movie=...) crashes on save

src/roboticstoolbox/backends/PyPlot/PyPlot.py

@@ -512,7 +512,8 @@ def getframe(self):
 
         # render the frame and save as a PIL image in the list
         canvas = self.fig.canvas
-        return _pil("RGB", canvas.get_width_height(), canvas.tostring_rgb())
+        image = _pil("RGBA", canvas.get_width_height(), bytes(canvas.buffer_rgba()))
+        return image.convert("RGB")
 
     def _push_inline_frame(self):
         # Push a snapshot into notebook output for inline animation.

src/roboticstoolbox/robot/BaseRobot.py

@@ -2058,6 +2058,9 @@ def plot(
 
         env = self._get_graphical_backend(backend)
 
+        if movie is not None:
+            from roboticstoolbox.backends.PyPlot import PyPlot
+
         launch_kwargs = {}
         for key in ("render_mode", "inline_every_n", "inline_format", "inline_dpi"):
             if key in kwargs:

tests/test_PyPlot.py

@@ -69,6 +69,36 @@ def test_launch_rejects_2d_axes(self):
             env.launch(fig=fig, ax=ax)
         plt.close(fig)
 
+    def test_plot_movie(self):
+        # robot.plot(..., movie=...) used to crash outright: BaseRobot.plot()
+        # referenced PyPlot in an isinstance check with no import anywhere in
+        # the module (NameError), and getframe() called the long-removed
+        # matplotlib Agg canvas method tostring_rgb() (AttributeError on
+        # modern matplotlib). Covers both bugs end-to-end via a real saved
+        # GIF, not just "no exception raised".
+        import tempfile
+        import os
+        from PIL import Image
+
+        panda = rp.models.Panda()
+        qt = rp.jtraj(panda.qr, panda.qz, 3)
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            path = os.path.join(tmpdir, "movie.gif")
+            env = panda.plot(qt.q, backend="pyplot", movie=path)
+            env.close()
+
+            self.assertTrue(os.path.exists(path))
+            with Image.open(path) as img:
+                n_frames = 0
+                try:
+                    while True:
+                        img.seek(n_frames)
+                        n_frames += 1
+                except EOFError:
+                    pass
+                self.assertEqual(n_frames, 3)
+
     def test_options_scalar_override(self):
         # Issue #418: options={"jointaxislength": ...} (a plain scalar
         # default, unlike the dict-valued color/linewidth options) used to